Town-wide Lakes Management Plan for the Town of Lewisboro Mark - PowerPoint PPT Presentation

Town-wide Lakes Management Plan for the Town of Lewisboro Mark Arrigo EcoLogic, LLC May 7, 2009

Scope  Summarize the water quality and aquatic habitat conditions of the Town’s Lakes  Develop a unified document to protect/improve water quality  Recommend specific actions

Outline  Lake Ecosystems  Lakes Impairment  Symptoms  Root causes & Sources  Reductions Needed  Management Options  Next Steps  Final Thoughts/Questions

Understanding Lake Ecosystems: The Importance of Nutrients  Focus on Phosphorus Limiting nutrient in most freshwater systems   Nutrients grow plants…  Algae– makes the water turbid  Rooted plants

Understanding Lake Ecosystems: The Importance of Nutrients  Trophic State  Defines the status of lakes from nutrient-poor, clear water state to nutrient-rich, very high biological productivity  Eutrophication  The process of moving from nutrient-poor to nutrient-rich conditions o A natural process that can be greatly accelerated by human activity

Lewisboro Lakes Impairment

Lakes Perception Summary CSLAP Perception Lakes Survey 2006 Excellent to slightly impaired; Waccabuc; Not quite crystal clear Rippowam Slightly impaired, definite algal Oscaleta “greeness” Slightly to substantially Timber; impaired Truesdale No data Kitchawan; Katonah

Lewisboro Lakes Algal Blooms Percent of Chlorophyll-a Measurements Exceeding Thresholds During Summer Period  Algae in water measured by Chlorophyll-a Lake N=12 Katonah  New York State Guidance Truesdale N=50 Lake Timber Lake N=21  Chloro-a > 15 ug/L = Notable Lake Impairment N=27 Waccabuc Lake N=26 Oscaleta  Chloro-a >30 ug/L = Severe Impairment Lake Nuisance bloom (greater than 30 ug/l) N=26 Rippowam Perceived Impairment (greater than 15 ug/l) Lake N=2 Kitchawan* 0% 10% 20% 30% 40% 50% 60% 70% 80% Percent *Lake Kitchawan represents two samples, one collected July 2007 and one collected August 2008. Both results were less than 15 ug/l.

Pollutant of Concern Algal blooms result from excessive phosphorus phosphorus Total Phosphorus vs Chlorophyll-a June 15 - September 15 Average 50 R² = 0.9442 40 Truesdale Chlorophyll-a (ug/l) Katonah (1999-2007) (2006-2007) 30 Waccabuc Oscaleta 20 (2002-2007) (2002-2007) Timber 10 (2005-2007) Rippowam Kitchawan (2002-2007) (2007) 0 0 20 40 60 80 100 Total Phosphorus upper waters (ug/l) Lake Result Perceived Impairment (<15 ug/l) Nuisance Bloom (>30 ug/l) Linear (Lake Result)

Take Away Message to This Point  Lakes are Impaired  Primary Impairment is from Algae  Poor water clarity  Pond scum  Algal blooms caused by excessive phosphorus

Where’s the Phosphorus Coming From: Primary External Sources?  Sources : Land use in the watersheds   Develop natural areas = >P to lakes Septics   Primarily from within 100m of waterways Point sources   Upstream lakes

Sources of Phosphorus: Results P from Land Use in Watershed  + P from Septics  + P from Point Sources  = Total External Phosphorus Load

Sources of Phosphorus: Lewisboro Lakes (Average) 7% 9% 22% 62% Point sources (upstream lakes) Development Natural land cover (forest, wetlands, etc) S eptic

External Sources of Phosphorus Phosphorus Loading Estimate, Lewisboro Lakes 100% 90% 80% 70% Contribution (kg/yr) 60% 50% 40% 30% 20% 10% 0% Rippowam Oscaleta* Waccabuc Truesdale* Kitchawan Katonah Timber Point Sources (upstream lakes) Estimated Septic - 100m buffer Land Cover - Human Activity Land Cover - Natural *Septic contributions for Oscaleta and Truesdale Lakes do not include possible contributions from Connecticut, therefore these values may be underestimated.

Additional Take Away Message  Septics are the primary source of phosphorus  Can’t restore/protect the lakes without addressing septics issue

Phosphorus Reductions Needed • Target concentration: 20 ug/l (currently: ~22 - 98 ug/L) • NYSDEC guidance value • selected based perceived water quality impairment for recreational use to total phosphorus concentration. Very aggressive controls Reduction needed to in developed areas Lake meet 20 ug/l (ex. BMPs) Eliminate Septic Oscaleta 9% 6% 29% Rippowam 27% 4% 68% Waccabuc 28% 4% 27% Kitchawan 46% 9% 72% Timber 52% 10% 75% Truesdale 63% 13% 65% Katonah 82% 9% 84% Assumes no new sources…..

Conclusions  Phosphorus is Primary Pollutant Septics are the largest contributor to P load  Soils mostly not suitable for septics  High density of houses near waterbodies  Septic systems aging   With no action eutrophication likely to accelerate  Significant reductions in phosphorus loading required

Management Options 1. Do nothing 2. “Maintain” current conditions 3. Improve water quality

1. Do Nothing  Rate of eutrophication will increase Septics will continue to deteriorate  Nonpoint from development will increase  More septics with development  Sedimentation will increase   End Result: greener and shallower lakes

2. “Maintain” Current Conditions  Implement Code revisions  Mandatory inspection/maintenance of septics Restriction on watershed development and landuse  near waterbodies  BMPs Focus on priority areas  Retention basins (stormwater)  Erosion controls   Public Education End Result:  Short term “stabilization” (variable)  Probable long term decline 

3. Improve Water Quality  Significantly reduce/eliminate septic contribution  Install Sewers in watersheds (Peach Lake example- next slide )  Holding tanks for more lightly populated areas  Code revisions  Restriction on most watershed development and landuse  Restrictions on fertilizers in watershed  Public Education  BMPs  End Result: Gradually improving water quality  Timeframe for improvement variable Groundwater transport 

Wastewater Treatment Peach Lake Example  1 Treatment plant : 120,000 gallons per day.  New York City Watershed : requires advanced level of treatment including: ammonia removal,  sand and membrane filtration, and ultraviolet disinfection.  Estimated project costs: Treatment plant: $10 million  Collection system: $14 million  Average cost per resident $1200 per year for 30 years  Compare to cost of maintaining septics…   Funding: Putnam County: $2.5 million  Westchester County: $10 million  NYCDEP: TBD (reimburse for the tertiary level of treatment estimated  to be $2.4 million)

Recommended Next Steps  Convene a public educational forum(s) to discuss current water quality, and future goals for the lakes of Lewisboro. Initiate Sewer Feasibility/Cost Study  Discuss creation of watershed tax districts to  help fund efforts Continue the expanded annual lakes monitoring  program and create a Lewisboro Lakes Report Card

Final Thoughts  It took over a century to get to this point you’re not going to restore the lakes overnight  This will not be easy or inexpensive  It will require long term planning and commitment from the community  With community support, it can be done!

Questions? Thank you,